In Windows Vista and 7 only the Ultimate and Enterprise versions have the feature which allows you to install a languagepack.
But in the other versions you can do the same thing using the console and regedit.

In order to install a new language (in this example de-DE and the languagepack is located in G:\langpacks\de-de\lp.cab) you have to do the following steps

Download the language pack in the language you want to install

Make sure that there is an lp.cab file inside the folder of the language pack

Open the Console (CMD) with administrator rights (Run as administrator)

Type the following commands (note that you have to set the correct path of your language pack)

Well as you already know I installed the final version (MSDN) of windows 7 two days ago and faced a few problems.
First of all there was this funny problem with the missing driver during the installation.

Well I try to summarize the good and bad news compared with the RCGood News

It is a little bit faster than the Release Candidate

Windows Media Player and Explorer are more stable and faster

Easy install of the language pack

Up to now I do not have the problem with unvisible windows (in the RC Version I had the strange problem that a window was no longer visible in the taskbar and ALT+TAB but after a while it came back)

In the Release Candidate I had also problems with memory leaks (especially Firefox) up to now I don’t have this problem

Generally the system seems to be very stable and fast

Bad News

The driver detection of the Release Candidate was much better (It found and downloaded every driver for my notebook but the final version did not. I had to do it manually.)

Sometimes the popup-preview of the taskbar does not show the image of the window (it just shows an icon)

I will update this list as soon as I have new good or bad news for the RTM.
But generally I can say that it is a very good operating system and that it is much better (faster) then vista